Check the datasheet ! (click !)
The answer is no.
Pin 9 (multiwatt) or 12 (PowerSO20) are INPUTS; you connect the 5 volt Arduino supply there.
They aren't power supply to external electronics.
Hmm, seems like i didn't understand what you were asking too.
The outputs are digital outputs.
If you supply the L298 with 12 volts, those pins will output something like 9 volts (twice the drop of a darlington transistor).
That's also true when you are controlling the motorspeed by sending a PWM signal to the Enable pins, although your multimeter will show some different voltage, that is is not what is actually happening.
You'd at least need a couple of capacitors to get something you have in mind.
I bet a better way would be to use a separate converter module, which can be had for a few bucks (really 2 dollars is about it).